Sizing agent for use in making paper

ABSTRACT

A neutral sizing agent of emulsion type to be added to paper pulp for facilitating the disaggregation and recovery of waste paper in making paper including paper board, said sizing agent being produced, for example, by dispersing in an aqueous emulsifying dispersion medium a polymerizable hydrophobic monomer such as styrene or 2-ethylhexyl methacrylate by using as an emulsifying dispersing agent a copolymer having units of one or more monomers given by the formula ##STR1## or ##STR2## wherein R is H or CH 3 , 
     X is a halogen atom, 
     A is a (C 2  -C 6 ) alkylene group, and 
     Y is an anion, 
     and a monomer given by the formula ##STR3## wherein R 1 , R 2  are H or CH 3 , and then subjecting the resultant dispersion to a radical emulsion polymerization.

The present invention relates to a sizing agent for paper making and,more particularly, to a so-called sizing agent which does not notablyadd to the wet strength of paper even when the use of a bonding agent islimited.

DESCRIPTION OF PRIOR ART

It is a well-known fact that, as a loading material for making paper,calcium carbonate has many advantageous features not only in itsproperties, but also from a viewpoint of economy. In the meantime, sincethe rosin sizing agent which is commonly used in paper making must beadapted for use under acid conditions, a paper making process in the useof calcium carbonate as a loading material cannot use the rosin sizingagent.

Nowadays, several "neutral" sizing agents which permit the sizing in analkaline zone have been proposed. For example, the U.S. Pat. No.3,694,393 discloses a method of preparing such a neutral agent asfollows:

"A method of adapting for use, as in making paper and the like, acopolymer of

(1) about 0.25% to 99.5% by weight of a monomeric material comprising apredominant amount of a compound of the formula ##STR4## and thecompound of the formula ##STR5## the symbols in the two formulas beingdefind as R is hydrogen or methyl,

X is iodine, bromine, or chlorine,

A is a (C₂ -C₆) alkylene group having at least two carbon atoms in achain between the adjoined O and N atoms or A may be a polyoxyethylenegroup of the formula (CH₂ CH₂ O)_(x) CH₂ CH₂ wherein x is at least 1,and

Y is an anoin, the latter compound being present in an amount up toabout one-third the weight of the former with

(2) at least one other monoethylenically unsaturaed monomer having agroup of the formula ##STR6## by bringing the copolymer at a solidsconcentration of about 25% to about 10% to a pH of 9 to 12 andmaintaining it at that pH for 1 to 5 hours at 5°-50° C."

However, according to said patent, since the sizing agent is used as awet strength modifier, it renders considerably difficult thedisaggregation and recovery of brokes produced in a paper mill.Generally in paper mills, since about 30% of ordinarily produced paperare recycled as brokes to the stock for reuse, it has been desired, inmaking paper which does not intentionally require a wet strength, toprovide such a sizing agent that does not particularly add to the wetstrength.

DESCRIPTION OF THE INVENTION

According to the present invention, a neutral sizing agent for papermaking is provided and, more specifically, provided is a neutral sizingagent of emulsion type which facilitates the disaggregation of brokeswithout increasing the wet strength when it is added to paper inprocess.

The sizing agent for paper making according to the present invention isobtained by dissolving in an aqueous medium a water-soluble cationiccopolymer compound having principal units of a monomer comprising apredominant amount of a compound given by the formula ##STR7## and aminor amount of a compound given by the formula ##STR8## wherein R is Hor CH₃,

X is a halogen atom,

A is a (C₂ -C₆) alkylene group, and

Y is an anion such as halogen ion (Cl⁻, Br⁻ or I⁻)

or an anion of an acid salt such as phosphate, acid phosphate, sulfate,bisulfate, methyl sulfate, carboxylate, sulfonate, sulfamate, acetate,formate, oxalate, acrylate, or α-methacryloxyacetate or, more,preferably, an anion of an acid having a ionization constant of 5.0 orless, namely, an anion of acid which is dissociated at a hydrogen ionand a monomer given by the formula ##STR9## wherein R¹ and R² is H orCH₃,

dispersing therein a polymerizable hydrophobic monomer such as styreneor 2-ethylhexyl methacrylate, and then subjecting the resultantdispersion to a radical emulsion polymerization.

Also, the sizing agent according to the present invention is obtained bydispersing a polymerizable hydrophobic monomer in an aqueous mediumcontaining as a principal emulsifying dispersing agent a water-solublecationic copolymer of the copolymer of the monomers given by saidformulas (1) and (2) with the monomer of said formula (3) and as anauxiliary emulsifying dispersing agent a compound given by the formula

    R.sup.3 --O--(CH.sub.2 --CH.sub.2 --O).sub.n SO.sub.3 M    (4)

wherein

R³ is a higher aliphatic or cycloaliphatic hydrocarbon residue,

n is an integer equal to or larger than 2, and

M is a monovalent metallic element or NH₄,

and then subjecting the resultant dispersion to a radical emulsionpolymerization.

As disclosed in the U.S. Pat. No. 3,678,098, the monomer given by saidformula (1) can be produced by causing a hydrogen acid salt of a basicester given by the formula

    H.sub.2 C═C(R)--C(O)--O--A--N(CH.sub.3).sub.2.HY

wherein

R is H or CH₃,

A may be a (C₂ -C₆) alkylene group interposed between adjacent oxygenand nitrogen atoms or a polyoxyethylene group given the formula (CH₂ CH₂O)_(x) CH₂ CH₂ wherein x is 1 to 11 or more, and

Y is a halogen or an anion of acid,

to react with epihalohydrin under acid conditions at room temperature to80° C., said basic ester being produced by copolymerizing an aromaticvinyl hydrocarbon such as styrene, a methacrylate such as dimethylaminomethacrylate and a nitrile compound such as azobisisobutyronitrile. Inthis case, the total amount of reactants is not converted into themonomer of the formula (1), but some units of the formula (2) areproduced along therewith. The relative amounts of the monomers (1) and(2) will vary depending on the reaction but, in typical, cases, theywill be present in roughly equivalent amounts, and it is known that asthe pH decreases the proportion of the monomer (2) decreases, while itincreases at neutral or in the alkaline side.

The water-soluble cationic copolymer compound constituting the principalcomponent of the emulsifying dispersing agent can be readily obtained bycopolymerizing one or more monomers given by the aforesaid formula (1)or (2) with the monomer given by the formula (3). Alternatively, it canbe produced by copolymerizing the monomer of the formula (3) with amonomer given by the formula ##STR10## wherein R is hydrogen or CH₃,

A is an (C₂ -C₆) alkylene group, and

Y is an anion similar to that of the formula (1) and (2),

and then causing the resultant copolymer to react with epihalohydrin at80°-85° C. under acid conditions and, more preferably, at pH 6 or less.

In producing the aforementioned copolymer, the principal component ofthe emulsifying dispersing agent according to the present invention maycomprise a water-soluble cationic copolymer compound which is obtainedby copolymerizing predominant amounts of those monomers given by saidformulas (1), (2), (3) and (5) with a small amount of othercopolymerizable monomers such as acrylic ester, methacrylic ester andaromatic vinyl hydrocarbon as added thereto as required.

For the purpose of use in the emulsifying dispersing agent according tothe present invention, the water-soluble cationic copolymer compoundpredominantly comprising one or more monomers given by the formula (1)or (2) and the monomer given by the formula (3) is sufficient. However,the use of a small amount of a compound given by said formula (4) incombination with a predominant amount of said water-soluble cationiccopolymer compound remarkably accelerates the emulsifying dispersion inthe aqueous medium, as shown in the preferred embodiment (7) to be givenlater.

The sizing agent for making paper according to the present invention isof an emulsion type which is obtained by emulsion-dispersingpolymerizable hydrophobic monomer in an aqueous medium containing apredominant amount of the emulsifying dispersing agent comprising theafore-mentioned water-soluble cationic copolymer compound and subjectingsaid monomer to a radical emulsion polymerization.

The radical emulsion copolymerization in an aqueous medium can bereadily effected by a well-known polymerization technique and anyspecial limit on the proportion of the emulsifying dispersing agent andthe polymerizable hydrophobic monomer is not required for the radicalemulsion polymerization reaction. However, in view of the stability ofthe emulsion as the sizing agent for making paper as well as fromeconomical considerations, a proportion in the range of 1:1 to 1:4 (byweight) is preferred.

Typical examples of the polymerizable hydrophobic monomers which can beused in the radical emulsion polymerization reaction include styrene,styrene derivatives, acrylic ester, methacrylic ester and otherhydrophobic vinyl compounds. The use of styrene or combination ofstyrene with 2-ethylhexyl acrylate is preferable.

The sizing agent for paper making of the present invention having thearrangement as mentioned herein-above is of an emulsion type having acationic property. Therefore, if it is added to anionic cellulosedispersed in water in the paper making process, it behaves as to beelectrically adsorbed by the cellulose molecules spontaneously. Thus, ifadded to the raw material of paper, namely, pulp slurry, the sizingproceeds spontaneously without using a bonding agent such as a sulfuricacid bond. In this manner, the sizing agent according to the presentinvention can serve as a neutral sizing agent.

Further, as will be shown in the experiments 1 and 2 to be describedlater, one of the specially advantageous features of the paper makingsizing agent according to the present invention consists in that arelatively large acount of addition thereof does not render difficultthe disaggregation of brokes as being found in the conventional neutralsizing agent, despite the fact that it exhibits at a smaller amount ofaddition thereof a sizing effect superior to that of the conventionalsizing agent.

Also, the paper making sizing agent according to the present inventioncan ensure almost perfect emulsification because the cationic copolymercompound is emulsion-polymerized with an equivalent or more amount ofthe polymerizable hydrophobic monomer and, therefore, it contributes tothe reduction in the amount of use of a nitrogen compound which isgenerally expensive. In this sense, the sizing agent according to thepresent invention is economically justifiable for paper making. Besides,the copolymerization of such a monomer as styrene eliminates thenecessity of any special operation in the disaggregation of brokes.

PREFERRED EMBODIMENT 1

In a four-port flask provided with an agitator, thermometer, refluxcondenser and dropping funnel, 1,000 g of isopropyl alcohol was preparedand heated to the reflux temperature. Then, a mixture of 780 g ofstyrene, 240 g of dimethylaminoethyl methacrylate and 20 g ofazobisisobutyronitrile was dropped over two hours into said isopropylalcohol kept at the reflux temperature. Thereafter, the mixture solutionwas subjected to polymerization reaction for five hours at 70°-80° C. tocomplete the reaction.

Then, after removing by evaporation about 750 g of isopropyl alcoholfrom the reactant solution, 92 g of acetic acid and 4,200 g of waterwere added thereto to be dissolved therewith and, further, 142 g ofepichlorohydrin was added thereto and the resultant solution was causedto react for three hours at 80°-85° C. As a result, a water-solublecationic copolymer compound A and a composition B corresponding to aneutral sizing agent of an aqueous solution containing about 20% of saidwater-soluble cationic copolymer compound A were obtained.

The copolymer compound A corresponds to the water-soluble cationiccopolymer compound constituting the emulsifying dispersing agent to beused according to the present invention, while the composition B can beused as the emulsifying dispersing agent according to the presentinvention as it is.

In a four-port flask provided with an agitator, thermometer, refluxcondenser and dropping funnel, 800 g of said composition B, 4 g ofHitenol (registered trade mark of Daiichi Kogyo Seiyaku Co., Ltd.,Japan) as an emulsifying dispersing agent given by the formula R³--O--(CH₂ --CH₂ --O)_(n) SO₃ NH₄ wherein

R³ is a higher aliphatic or cycloaliphatic hydrocarbon residue, and

n is an interger equal to or larger than 2,

700 g of tap water, 240 g of styrene, 80 g of 2-ethylhexyl acrylate and24 g of aqueous solution of hydrogen peroxide (H₂ O₂, 35%) were preparedand subjected to polymerization reaction for six hours at 70°-80° C.and, then, cooled to complete the reaction. As a result, 1,840 g of theneutral sizing agent of emulsion type I according to the presentinvention was obtained (25.8% solid content, viscosity 25 cps (30° C.)).

PREFERRED EMBODIMENTS 2 THROUGH 8

800 g of the composition B used in the preferred embodiment 1 was usedas the emulsifying dispersing agent, while 700 g of tap water was usedas an aqueous medium and a polymerizable hydrophobic monomer wasdispersed therein. Then, the resultant dispersion was caused to react ina manner almost identical to the preferred embodiment 1. Consequently,emulsion type neutral sizing agents II through VIII were obtained fromvaried kinds and amounts of polymerizable hydrophobic monomers andpolymerization initiators used.

The proportions of components and other polymerization conditions in thepreferred embodiments 2 through 8 are summarized in Table 1 togetherwith those in preferred embodiment 1.

                                      Table 1*.sup.1                              __________________________________________________________________________    Preferred           Polymerizable hydrophobic agent                           embodiment                                                                           Emulsifying dispersing agent                                                                    2-ethylhexyl                                                                         Lauryl Polymerization initiator                                                                Sizing                       No.    Composition B                                                                         Hitenol*.sup.2                                                                     Styrene                                                                            acrylate                                                                             methacrylate                                                                         TBHPO*.sup.3                                                                        H.sub.2 O.sub.2 *.sup.4                                                           agent                        __________________________________________________________________________    1      800     4    240  80                  24  I                            2      800          240  80            8         II                           3      800          160  160           8         III                          4      800          320                8         IV                           5      800     8    240  80            8         V                            6      800     4    240  80            8         VI                           7      800     4    240         80     8         VII                          8      800     6    360  120           12        VIII                         __________________________________________________________________________     *.sup.1 Values are given by weight in gram (g).                               *.sup.2 Registered trade mark of Daiichi Kogyo Seiyaku Co., Ltd.              *.sup.3 Tertiarybutyl hydroperoxide                                           *.sup.4 35% aqueous solution                                             

Hereinafter, the results of test No. 1 performed for evaluating thesizing effect of the paper making sizing agents I through VIII accordingto the present invention obtained in the aforementioned preferredembodiments 1 through 8 will be presented.

TEST 1

To paper stock slurry (containing 2% of air-dried pulp and 0.6% ofcalcium carbonate) comprising beaten pulp (130 cc of L-BKP canadianStandard Freeness) and calcium carbonate as the loading agent), one ofpaper making sizing agents I through VIII according to the presentinvention obtained in the aforementioned preferred embodiments 1 through8 so that 0.5% of solid content of the sizing agent exists per 100% ofair-dried pulp. Then, the slurry was sized and fed into a manualsheeting tester (trade name, TAPPI Standard Sheet Machine, Toyo SeikiCo., Ltd., Japan) to obtain 45 g/m² of manually-sheeted paper in theusual manner.

For the purpose of comparison, the Stechihid sizing degrees of theresultant manually-sheeted paper are summarized in Table 2 along withthose of manually-sheeted paper obtained in the same manner from theaforementioned composition B which can be regarded as a well-knownneutral sizing agent.

                  Table 2                                                         ______________________________________                                        Types of sizing agents                                                                         Stechihid sizing degree (sec.)                               ______________________________________                                        Composition B    1.2                                                          I                5.8                                                          II               3.1                                                          III              2.4                                                          IV               1.7                                                          V                2.6                                                          VI               2.9                                                          VII              1.7                                                          VIII             2.1                                                          ______________________________________                                    

TEST 2

To prepare stock slurry (containing 2% of air-dried pulp and 0.6% ofcalcium carbonate) comprising beaten pulp (200 cc of L-BKP CanadianStandard Freeness) and calcium carbonate as loading material, variedamounts of the paper making sizing agent I according to the presentinvention obtained in the aforementioned preferred embodiment 1 wereadded and, also, a varied amounts of said composition B were added forthe purpose of comparison to the same slurry, to manually sheet paper inthe similar manner to the aforesaid Test 1.

The Stechihid sizing degree of the resultant manually sheeted paper andthe results of the pen-writing test according to the TAPPI paper pulptesting method No. 12 and the disaggregation tests are summarized inTables 3 through 5.

                  Table 3                                                         ______________________________________                                        (0.35% of solid content of sizing agent existing per                          100% of air-dried pulp)                                                                  Stechihid sizing                                                                          Pen-writing                                                                             Disaggregation                               Sizing agent                                                                             degree (sec.)                                                                             test      test (sec.)                                  ______________________________________                                        Composition B                                                                            0           0         30                                           I          0.5         1         30                                           ______________________________________                                    

                  Table 4                                                         ______________________________________                                        (0.5% of solid content of sizing agent existing per                           100% of air-dried pulp)                                                                  Stechihid sizing                                                                          Pen-writing                                                                             Disaggregation                               Sizing agent                                                                             degree (sec.)                                                                             test      test (sec.)                                  ______________________________________                                        Composition B                                                                            5.5         3         90                                           I          8.2         4         40                                           ______________________________________                                    

                  Table 5                                                         ______________________________________                                        (1% of solid content of sizing agent existing per                             100% of air-dried pulp)                                                                  Stechihid sizing                                                                          Pen-writing                                                                             Disaggregation                               Sizing Agent                                                                             degree (sec.)                                                                             test      test (sec.)                                  ______________________________________                                        Composition B                                                                            18.3        5         180                                          I          18.2        5-6       60                                           ______________________________________                                         *In the disaggregation test, 2g of manually sheeted paper chips was           immersed in 150cc of warm water at 50° C. and agitated by a mixer      for home use, and the time elapsed until the paper chips were                 disaggregated and dispersed into their initial slurry state was measured.

What is claimed is:
 1. A method of producing a sizing agent for makingpaper comprising the steps of:preparing a water-soluble cationiccopolymer compound by reacting a first monomeric material containing apredominant amount of a compound of the formula ##STR11## and a minoramount of a compound of the formula ##STR12## the symbols in the twoformula being defined as R is hydrogen or CH₃,X is a halogen atom, A isa (C₂ -C₆) alkylene group, Y is a halogen ion or an anion of acid saltsuch as phosphate, acid phosphate, sulfate, bisulfate, methyl sulfate,sulfonate, sulfamate, acetate, formate, oxalate, acrylate, orα-methacryloxyacetate, with a second monomer of the formula ##STR13##wherein R¹ and R² are H or CH₃, for about five hours at pH 6-5 and80°-85° C.; and dispersing in an aqueous emulsion dispersion of saidcopolymer compound a polymerizable hydrophobic monomer of said secondmonomer at a ratio of 1:1-1:4 (by weight) causing the resultantdispersion to react at pH 6 or less and 70°-80° C. for six hours byusing a polymerization initiator to subject said dispersion to a radicalemulsion polymerization.
 2. A method of producing a sizing agent formaking paper comprising the steps of:preparing a water-soluble cationiccopolymer compound by reacting a first monomeric material containing apredominant amount of compound of the formula ##STR14## and a minoramount of a compound of the formula ##STR15## the symbols in the twoformula being defined as R is hydrogen or CH₃,X is a halogen atom, A isa (C₂ -C₆) alkylene group, Y is a halogen ion or an anion of acid saltsuch as phosphate, acid phosphate, sulfate, bisulfate, methyl sulfate,sulfonate, sulfamate, acetate, formate, oxalate, acrylate, orα-methacryloxyacetate, with a second monomer of the formula ##STR16##wherein R¹ and R² are H or CH₃, for about five hours at 80°-85° C.;adding to said copolymer compound a small amount of an auxiliaryemulsifying agent given by the formula

    R.sup.3 --O--(CH.sub.2 --CH.sub.2 --O).sub.n SO.sub.3 M    (4)

whereinR³ is a higher aliphatic or cycloaliphatic hydrocarbon residue, nis an integer equal to or larger than 2, and M is a monovalent metallicelement or NH₄, to prepare an aqueous emulsion dispersion; and adding tosaid aqueous emulsion dispersion a polymerizable hydrophobic monomer ofsaid second monomer at the ratio of 1:1-1:4 (by weight) of saidcopolymer compound and subjecting the resultant dispersion to thepolymerization reaction in the existence of aqueous solution of hydrogenperoxide for six hours at 70°-80° C.